Add support to specify where go builds the app and optionally skip dependency fetching

What does this MR do?

• Add GOSEC_GO_PKG_PATH variable for telling the analyzer where to compile the go app.
• Add COMPILE variable for optionally skipping dependency fetching (when users wish to handle GOPATH manually)
• Change dependency fetching to download only, no need to build/install by default

What are the relevant issue numbers?

gitlab-org/gitlab#330678 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer